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The Marine Boiler.

A A. The combustion chambers are also variously divided, there
being from one to four per boiler; two are shewn at G G, each
having a plate c, to split and assist the draught. The heated
gases, rising from the fire at A, pass through the combustion
chamber G and tubes D, to the uptake, which is placed at E to
cover the tubes. The boiler is cylindrical, but with large flat
ends which require a good deal of stiffening, for flat portions in
all boilers are weak. There are two belts of shell plates i inch
thick, the first H and the second j, each being, on account of its
large circumference, divided into three, and connected by double
butt-straps, with treble riveting, as in plan at K The division is
uniform and is seen on the front elevation; where F F F represent
the joints of the first, and B BB those of the second plate. The
circumferential seams are double riveted, as at L L, and the man-
hole is placed at M, with strengthening ring. Sometimes a
separate dome is connected to the top of the second plate, but
just as often the steam valve is applied direct to the boiler; in any
case the dome is simply a horizontal cylinder with dished ends.
The front and back-plates are divided into three, N, o, and P shew-
ing the parts of the front-plate, while Q, R, s are those of the
back-plate. N, P, Q and s are each f- inch thick, but R is only f inch,
and o is \\ inch. They are all flanged and riveted as shewn, o
being cut out a suitable shape to take the nests of tubes, while R
is rectangular. Where three plates overlap, the middle thickness
is drawn out as shewn at sz, which is a plan of the joints XT.
Longitudinal stays, for the steam space, are supplied by bolts
u XT, having large washers to distribute the pressure The plate o
is necessarily* stiffened by double thickness at the seams, but there
are also stiffening plates vv riveted on the inside, and stay tubes
w w, shewn by their nuts, support both plate o and combustion
chamber tube-plate x. The other tubes, ferraled at the firebox
end, and expanded at the uptake end, act also as stays. The plate
i? is stayed by bolts at Y Yl9 and the manholes are stiffened by
riveted plates at z. The three bolts marked YX pa$s right through
to the back-plate s, which is further strengthened, together with R,
by' screwed stays at a, which are bolts screwed their whole length
and fitting into holes tapped in the plates, The
chamber back-plate J inch thick, shown at G, is a' simple